This invention relates to dynamoelectric machines such as doubly-fed reluctance motors (DERM's) and, more particularly, to a sensorless control scheme for operating such motors.
Despite recent advances in AC adjustable speed drive (ASD) technology, the cost the power converter used in such drives remains the largest contributor to the overall cost of an ASD system. This, in turn, prevents wider industrial applications of these systems. Slip power recovery techniques used in wound-field induction machines have managed to reduce converter ratings and their attendant cost. Applicability of such machines in pump-type applications, where variations in motor speed are limited, would therefore be advantageous. However, the high cost and bulkier size of these wound-field machines, together with the maintenance required for the slip rings used in them, have unfortunately limited their application.
Brushless and cageless wound-field induction motors have been proposed, but these concepts have only recently begun being seriously investigated. It is a feature of these motors to move the secondary motor minding onto the stator. Slip rings are eliminated using this approach; but slip power recovery control, i.e., what is commonly referred to as "double feeding"control, can still be implemented. For pump-type applications, this is an attractive, and cost effective approach. One type motor under consideration is a doubly-fed reluctance motor, or DERM. An advantage of this type motor, which has simple saliency on its rotor, is its structural simplicity. This translates both into a higher efficiency and lower cost motor. In analyzing the performance of DERM's, it has been found that they behave the same as a non-salient synchronous machine, and they can replace existing 1-25Hp. industrial induction motors which operate in the 0-1800Rpm. range. This range is set by limiting the magnetizing inductance of the motor to 2.0-2.5p.u. If a machine is allowed a larger than normal airgap, larger machines can be used. This is particularly useful in sealless pump applications.